This application contains subject matter which is related to the application entitled xe2x80x9cProcess To Determine The Response Pressure Of A Brake In A Vehicle Braking Systemxe2x80x9d by the instant inventors which is being filed concurrently herewith.
The present invention relates to a process for braking a vehicle containing at least two brakes actuated by an energy supply. As used herein, the term xe2x80x9cenergyxe2x80x9d is not to be taken in the strictly physical sense, but as a collective term for all media which cause a brake to produce a braking force when supplied to the brake.
The term xe2x80x9cbrakexe2x80x9d as used herein includes not only an individual module which produces a braking force directly, but also a plurality of such modules. Also included by the term xe2x80x9cbrakexe2x80x9d can be the system components such as actuating, control and transmission devices belonging to one or several such modules downstream of the operating element (e.g., the brake pedal) actuated by the driver of the vehicle. A xe2x80x9cbrakexe2x80x9d in the sense of the invention therefore also refers to a braking circuit as part of the vehicle braking system or the complete braking system of a vehicle in a vehicle train.
When energy is supplied to a brake, starting with the inactive state, the production of a braking force by the brake (i.e., the response of the brake) begins only when the energy attains a certain value. This value is referred to as the response energy of the brake. It is dependent on response resistances of the components producing the braking force directly and, if applicable, the system components installed between them and the energy detection point. The response resistances may be due, for example, to friction and to restoring forces, such as the force of a return spring.
Depending on their construction, the brakes of a vehicle may have different response energies. In such case, and when partial braking takes place, i.e., braking with low utilization of the total energy available to the brakes, the brake with the highest response energy, i.e., the brake which responds last, is significantly less strained than the brake(s) with lower response energy which respond earlier. Since most braking applications by far are partial brake applications during the operation of a vehicle, greater wear of certain parts, in particular, the brake linings, brake drums, and brake disks, occurs in the earlier-responding brake(s) due to higher strain.
It is the object of the present invention to improve the process for braking a vehicle containing at least two brakes so that a more even wear of all brakes is ensured.
This object is achieved by the present invention which provides a process for braking a vehicle having at least first and second brakes, comprising supplying energy to said first and second brakes so as to actuate them, said energy being distributed between said first and second brakes in accordance with the response energies of said first and second brakes. Preferably, a momentary value of the response energy of at least one of the brakes is used for distributing the energy. The momentary value of the response energy of the brake may be determined as follows:
(a) measuring the existing vehicle deceleration to determine a value of ground-vehicle deceleration,
(b) supplying a braking test energy to the brake being tested,
(c) measuring the deceleration of the vehicle after the braking test energy has been supplied to the brake being tested in order to determine a value of vehicle test deceleration,
(d) comparing the value of ground-vehicle deceleration with the value of vehicle test deceleration, and
(e) if the value of vehicle test deceleration is greater than the value of ground-vehicle deceleration by more than a predetermined tolerance value, repeating steps (a) to (d) with a reduced braking test energy until the difference between the value of vehicle test deceleration and the value of ground-vehicle deceleration is decreased to no more than the predetermined tolerance value, or
(f) if the value of vehicle test deceleration is equal to or less than the value of ground-vehicle deceleration, repeating steps (a) to (d) with a higher braking test energy until the value of vehicle test deceleration exceeds the value of ground-vehicle deceleration by a value which is less than or equal to the predetermined tolerance value.
The response of the brakes at different times due to their different response energies may have a detrimental influence on the travel stability of the vehicle. The invention eliminates this possibility.
The solution provided by the invention can consist in practice of supplying different amounts of energy to the different brakes at the outset so that all of the brakes respond simultaneously.
The invention can be carried out with any form of energy which is used to apply the brakes, e.g., with electrical energy or with pressure. In case pressure is used to energize or actuate the brakes, liquid or gaseous energy carriers, e.g., compressed air, may be employed.
The response energies of the different brakes can be determined in any desired manner, e.g., as described further below as the momentary value(s) of the response energy or energies, or in the usual way, by means of a roller testing stand. In the latter case, the brake to be examined is supplied with energy, starting from an unactuated state, until the roller testing stand detects a first braking force. The energy indicated at that moment by an appropriately placed measuring instrument is the response energy.
Instances may occur, however, where the response energy of one or several brakes change during the operation of the vehicle. This may due, for example, to the maintenance and state of repair of the affected brake(s), to changes in material characteristics, as well as to changes in the brake layout. A change in the response energy may also occur, for instance, when a vehicle train consists of a motor vehicle and one or several trailers, wherein the trailers may be changed from time to time. Such case may be an example for changes in the brake layout.
In order to ensure the attainment of the advantages provided by the invention in such cases, the invention can be further developed so that it provides for the ascertainment of the momentary value(s) of the changing response energy or energies during one or several brake applications, basing the distribution of energy to the brakes on these momentary values.